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    <a href="../index.html">cppreference.com</a> &gt; <a href=
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    log
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    Syntax:
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  <pre class="syntax-box">
  #include &lt;math.h&gt;
  double log( double num );
</pre>

  <p>The function log() returns the natural (base e) logarithm of
  <em>num</em>.  There&#39;s a domain error if <em>num</em> is
  negative, a range error if <em>num</em> is zero.</p>

  <p>In order to calculate the logarithm of <em>x</em> to an arbitrary
  base <em>b</em>, you can use:</p>
  <pre class="example-code">
  double answer = log(x) / log(b);
</pre>

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    Related topics:
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    <a href="exp.html">exp</a><br>
    <a href="log10.html">log10</a><br>
    <a href="pow.html">pow</a><br>
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